Cantu: I think they’re a huge step in the right direction. As you know, when we wrote our book Concussions and Our Kids in 2012, we asked that there be no heading in soccer until the age of 14. That also has been the focus of a combined effort between the Concussion Legacy Foundation and the Institute of Sports Law and Ethics at Santa Clara University and the Safer Soccer Campaign that Brandi Chastain and Cindy Parlow Cone have been the immediate persons with and which recently has been joined by Taylor Twellman.

I think [the new U.S. Soccer heading guidelines] are a great step in the right direction. I obviously would have preferred them to extend it up through the age of 13 and let the limited heading occur in high school. But I’m a realist, and this is a huge change and a change in the right direction. It has eliminated over a period of time hundreds of thousands of sub-concussive and concussive blows in youngsters whose brains are most vulnerable.

So it’s much better than what it was when they were trying to head soccer balls at ages 5, 6, 7, 8, 9 and 10. Would it be better that they not head them at 11, 12, or 13? Yes. But the fact it’s being limited in practice through those ages is better than no limitation.

Cantu: No, because the issue is not primarily correctly heading the ball. Yes, to head it improperly you can get greater acceleration forces to the head. But we’re primarily not heading the ball at these young ages not because of the impact from the ball, but because in the act of heading the ball, heads collide. And heads collide with other body parts. Not intentionally. Quite the contrary, very accidentally.

So proper technique is not going to eliminate the concussions that happen because heads collide, because you didn’t see the other head coming. So I understand what he’s saying, but he’s missing the point. These rules changes are not being put into effect primarily to eliminate soft soccer balls contacting a youngster’s head. Though there is some issue with subconcussive blows, it’s totally a separate one. But the major thing is you’re eliminating heads colliding and heads colliding with elbows and shoulders and so on. That’s how the concussions happen.

SI.com: The second tweet comes from James Galanis, the personal coach to Carli Lloyd and a former women’s pro league coach:

Not being allowed to practice heading at training for ages 11 to 13 but allowing players to head ball in games equals even more concussions.

Cantu: No, I don’t believe that’s correct at all. First of all, the skills of heading don’t necessarily require you to do it in a game situation. You can be taught in a practice situation and you can be taught with a lighter ball than a regulation soccer ball, so that the subconcussive aspect of things can be greatly minimized. So you can still be taught some of these skills in a controlled environment where heads can’t collide. It’s the heads colliding and heads colliding with other body parts that primarily you want to eliminate. And I think that simply backing it up to ages 11 to 13 before you start to do this is going to save a lot of concussions that otherwise would have happened—and a lot of head trauma that otherwise would have happened.

Scott J. Ferrell/CQ-Roll Call Group/Getty Images

SI.com: Are you surprised by the amount of backlash to these new rules from players and coaches?

Cantu: No, I’m not the least bit. Because the backlash has been there from the get-go three years ago when we started to get on this campaign of getting rid of tackle football under 14. At the time we wanted full body-checking in ice hockey to be from age 14. At the time we started it, it was 11, and now it’s 13, so it’s almost there. It’s rather encouraging to see ice hockey made the first move, and now soccer has made the second.